The present invention is directed to phytoremediation in general, and more specifically to incorporating the use of a remediation-assisting or treatment material within a vegetation remediation system in order to enhance the remediation of contaminated soil and groundwater in the vicinity of the vegetation.
Phytoremediation refers to the use of vegetation in the remediation of contaminated soil and groundwater. It is emerging as the remediation technology of choice when it is feasible to use as a primary or secondary system. The natural ability of vegetation to clean contaminants from soil and groundwater is of great benefit to the environment and society. It is effective and relatively inexpensive to use and the natural setting created by it renders this technology highly desirable.
U.S. Pat. Nos. 5,829,191 and 5,829,192 to the inventor herein disclose unique phytoremediation techniques, as does U.S. Provisional Application Ser. No. 60/066,678, filed Nov. 26, 1997 and Ser. No. 60/075,473, filed Feb. 20, 1998. These techniques improve the remediation of contaminants by vegetation by increasing effectiveness and/or decreasing expense. These patents and applications are incorporated herein by reference as if fully set forth.
Of course, remediation technologies and techniques other than phytoremediation must also be considered as well. Many other technologies and techniques remain effective, inexpensive and in some applications necessary.
By way of example, U.S. Pat. No. 5,266,213 to Gillham describes a technique for treating contaminated groundwater in an aquifer, i.e, water from deep underground, by excavating a trench with a trench-cutting machine and placing a homogeneous mixture of sand and iron filings in the trench. The permeability of the iron-sand mixture should not be lower than that of the aquifer itself so that the flow of water is not impeded by the mixture. The iron must be placed in the trench so that no oxygen can reach it, thus the iron must be buried within the trench. Otherwise, accessibility to oxygen will rust the iron and it will become ineffective to promote the breakdown of contaminants. The iron must be exposed to the groundwater for a "residence time," about one to two days. Alternatively, a tank or pond is provided at the surface of the remediation site, and contaminated groundwater is drawn out of the soil by means of a pump and fed into the pond which contains a body of iron filings or a mixture of iron fillings and sand. In either arrangement, the water slowly percolates through the iron fillings of the mixture for the residence time, and certain contaminants-halogenated-are broken down chemically.
The techniques in the Gillham patent require considerable labor, and the results and applications are limited. By way of example, it may be difficult to match the aquifer flow characteristics to prevent blockage or to channel for possible redirection of the groundwater flow. Also, there is a potential for the iron to transform and cause secondary reactions in the barrier wall or downgradient from the barrier wall that may cause the aquifer to become clogged, become contaminated with elevated levels of iron in solution or cause other reactions to occur that might prove deleterious. Moreover, there may be incomplete contaminant degradation. The Gillham system relies on the need to provide an adequate residence time for total degradation of the halogenated compounds. If that residence time changes because of changes in the groundwater flow or the physical or chemical dynamics of the iron barrier, an incomplete reaction could occur that would allow derivative contaminants to escape the iron barrier. Such derivative contaminants (e.g., vinyl chloride) could be more toxic than the contaminants which were to be treated.
The present invention marries the phytoremediation technology with other technologies for remediating contamination in soil and groundwater. In doing so, a single system can be more effective in remediating at least particular contaminants. Those contaminants not necessarily removed by any of the discrete technologies can through the use of the techniques in accordance with the present invention be removed or at least substantially removed.